London - Women who exercise during pregnancy and then breastfeed may be able to better protect their children from conditions such as diabetes and heart disease.
Those who manage more daily steps during pregnancy have healthier breast milk, a study suggests.
Researchers used fitness trackers to see how active 139 women were at around three, six and nine months pregnant.
Those who took more exercise – even of moderate intensity – had higher levels of an important sugar called 3-sialyllactose (3SL) in their breast milk. The researchers also found that mice given breast milk high in 3SL from active mothers had less body fat, healthier hearts and better control of their blood sugar.
That might help explain why breastfed children appear to have a lower risk of becoming obese and developing diabetes in later life. The findings suggest women who breastfeed may give their babies even greater health benefits if they have stayed active during pregnancy.
Researchers say 3SL could be added to formula milk, so children of women unable to breastfeed could also benefit.
Lead author Dr Kristin Stanford, from Ohio State University in the US, said: "The increases in 3SL were not necessarily related to exercise intensity, so even moderate exercise like a daily walk is enough to reap the benefits.
"Exercise is also great for your overall health during and after pregnancy. Getting moving is going to benefit both you and your baby." The study, published in the journal Nature Metabolism, used fitness trackers on a group of healthy recruits with an average age of 30.
The more physically active the women were and the more daily steps they took, the more 3SL tended to be in their breast milk when this was tested two months after they gave birth. Those with a lower body mass index also had higher average levels of 3SL. It would be unethical to prevent pregnant women getting exercise to see what effect this has on their children’s health in later life, so the researchers instead did an experiment on mice, which also produce 3SL in their milk.
They found year-old mice given milk from females that had run on a wheel were a lower weight than mice given milk from inactive females. They also had less body fat and better heart function.
The results led the researchers to conclude that it was the breast milk – specifically higher levels of 3SL in the breast milk – that helped to keep the mice healthy.
Scientists do not yet understand how exercise might increase levels of 3SL. However, it is one of the oligosaccharides – small sugars which make up five to 15 percent of human breast milk, but only 0.5 percent of cow’s milk. That could explain why babies given formula milk, which usually contains cow’s milk, may miss out on some health benefits from breastfeeding.